The long term objective is to achieve a better understanding of the association cortex and its relation to the primary sensory cortex. The neocortex is the highest level of the brain and the study therefore has implication for mental health. The starting point for the proposed research is the discovery that association cortex as well as the sensory cortex is the target of sensory pathways that are relayed by the dorsal thalamus. The questions raised in the specific aims concern differences in the primary and secondary pathways. Each pathway is influenced, but not in the same way by centers in the brain stem that are not modality-specific -- the reticular formation and the reticular nucleus. The aim is to identify the functional significance of the modulating influences and their differences. The targets of the secondary pathways in the cortex and the cortical layers of terminations must be identified to understand the relation between sensory and association cortex inasmuch as the areas called "association cortex" receive thalamic projections from the secondary pathways. Cortico-cortical connections and descending projections from cortex can be viewed as the basis for integration between primary and secondary pathways.